Both Silicon Carbide (SiC) and Silicon (Si) are semiconducting materials that are used to create products such as memory, light emitting diodes (LEDs), micro-electro-mechanical systems (MEMS) and other types of devices. Crystalline SiC is the material of choice for MEMS transducers when device reliability in extreme environments is a primary concern. However, due to both the high cost of bulk SiC wafers, and their expensive bulk micromachining processes, the use of SiC has been limited to only a few applications, typically those found in the aerospace industry.
However, as described in International Patent Application No. PCT/AU2010/000153 (published as WO2010/091473), entitled “A chemical vapour deposition system and process”, a new type of SiC growth reactor was recently developed, allowing the deposition of thin, high quality epitaxial layers of SiC onto Si wafers up to 300 mm in diameter. This breakthrough has opened up the opportunity for Sic-based devices to be produced with superior performance at a reasonable cost.
Thin film epitaxial SiC on Si has a vast potential for MEMS, as it enables the realization of advanced micro-transducers that benefit from the mechanical properties of the SiC on low-cost Si substrates through established fabrication processes (including silicon micromachining). In addition, Si wafers with diameters up to 300 mm are now readily available, contributing to the overall reduction of device production costs.
In addition to the above, the relatively new material graphene, consisting of a two-dimensional sheet of carbon, is currently an extremely active area of research due to graphene's many desirable properties (including extremely high fracture strength and electrical and thermal conductivities, lubrication properties, optical thinness (making the graphene appropriate for electronic screens), and excellent functionality (for sensors).
However, existing methods for forming graphene suffer from a number of difficulties. For example, micromechanical exfoliation of graphene requires careful use of adhesion tape to peel individual sheets of graphene from bulk graphite. This process is time consuming, is only suitable for single devices, and the thickness distribution of the exfoliated graphene layers cannot be controlled. In an alternative process, high temperature sublimation of carbon from bulk crystalline SiC produces high quality films compatible with semiconductor fabrication methods, but bulk SiC wafers are extremely expensive, and the sublimation process is incompatible with SiC on Si substrates due to the high temperatures required. Finally, Chemical Vapor Deposition (CVD) growth of graphene on metal foils produces very high quality graphene films, however an additional process step is than required to transfer the graphene from the metal foils and onto the desired substrates. Moreover, the process is incompatible with standard semiconductor fabrication methods.
It is desired to provide a process for forming graphene that alleviates one or more difficulties of the prior art, or that at least provides a useful alternative.